Cancer risk and surveillance in IBDDownloads

A 38-year-old man presents with concerns after finding out that his father was recently diagnosed with colon cancer. Family history is only significant for his paternal grandfather who also had colon cancer. A screening colonoscopy is performed, and a polyp is found in the ascending (proximal) colon, which on biopsy shows adenocarcinoma. A mutation in a gene that is responsible for which of the following cellular functions is the most likely etiology of this patient’s cancer?

A 72-year-old man presents to the emergency department with a complaint of rectal bleeding. He describes blood mixed in with the stool, which is associated with a change in his normal bowel habit such that he is going more frequently than normal. He also has some crampy left-sided abdominal pain and weight loss. His symptoms started 2 months ago, but he thought they are due to lack of dietary fiber intake and excess consumption of red meat. He has had type 2 diabetes mellitus for 35 years for which he takes metformin. He also uses daily low-dose aspirin for cardioprotection and occasional naproxen for knee pain. His family history is irrelevant. On examination, his abdomen and digital rectal examination are normal. Colonoscopy shows an ulcerating mucosal lesion with a narrow bowel lumen and biopsy shows a moderately differentiated adenocarcinoma. Which of the following is the greatest risk factor for colorectal cancer in this patient?